The defending champion turned on the power to beat Joe Perry 13-11 after flirting with defeat for much of the match.

He later revealed he had benefitted from a chat with renowned psychologist Dr Steve Peters after telling him not to travel to Sheffield earlier in the week so he could concentrate on his work with Brendan Rodgers' men.

O'Sullivan told BBC Sport: "Obviously Liverpool are going for the Premier League and I know how important that is for him and for the Liverpool people.

"I have got friends from Liverpool and it would be so great if they can do it, so I'm mindful that I don't want to take all his time up.

"I said, 'That's more important, I'm going to be okay', but really I made a mistake. I could have done with him here on Thursday.

"But he said he's not going to make that mistake again, he's going to be around a bit more now."

O'Sullivan, who trailed 7-9 overnight and 9-11 at the mid-session interval, rattled off four successive frames as he hit top form to book his place in the last eight.

The title favourite made no mistake to capitalise on a series of errors by Perry, producing masterful back-to-back century breaks to clinch victory as he gradually turned the screw.

O'Sullivan never led in the match until he claimed the penultimate frame with a break of 124, but once in front, he took full advantage, sealing victory with another of 113.

He won the first frame of the session 87-16 and after Perry had re-established his two-frame lead in the next with his opponent calling a foul on himself, compiled a break of 82 to stay in touch.

But Perry refused to wilt and eased himself to within two frames of victory by claiming the 20th by 81 points to 39.

However, it was then that O'Sullivan made his move, clinching the next two with breaks of 53 and 52 before turning on the style to take himself over the finishing line.

Perry said: "I'm understandably gutted. I gave it everything over the three sessions and I have got no regrets over anything I did.

"I gave everything. I was fully committed to every shot I played, I still felt calm and relaxed at the end, so I did everything I could.

"I just ran into an absolute genius at the end, so what can you do?"

O'Sullivan will face either Shaun Murphy or Marco Fu in the quarter-finals, and Alan McManus will hope to join him after taking control of his last 16 clash with Ken Doherty before the Irishman staged a fightback.

Leading 4-3 overnight, McManus claimed the first six frames of the morning session to take himself to within three of victory before Doherty stemmed the tide with a break of 93 to reduce the deficit to 10-4.

He took the next too, 88-0 in a single visit to the table to end the session on a positive note, but faces an uphill task when the match resumes on Saturday evening.

Judd Trump, the former world number one and a semi-finalist last year, reeled off four straight frames to finish the first session with a 6-2 lead over Ryan Day.

The 24-year-old was twice pegged back by Day after leading 1-0 and then 2-1 before pulling clear as he started to hit form.

Trump took the fifth frame by a single point, but runs of 76 in the next and 78 in the eighth saw him establish a four-frame advantage.

The Bristol cueman outscored his opponent by 230 points to 14 in those final three frames.